1. Field of the Invention
The invention pertains to the field of porous media. More particularly, the invention pertains to a method of measuring the pore structure of the individual layers in multi-layered composite porous materials.
2. Description of Related Art
Multi-layered porous materials and functionally graded porous materials with gradually changing pore structure are being increasingly used for high technology applications. The effectiveness of such materials depends upon the pore structure of individual layers, however, currently available techniques are incapable of providing a measurement of the pore structure of individual layers of a multi-layered composite material. For example, porosimetry only measures the pore volume and pore volume distribution of the entire composite. Moreover, in many of the composite filters, one of the layers is very thin and the low pore volume associated with this layer is not detectable by porosimetry. Flow porometry measures the size of the constricted part of the pores in the entire composite. Unfortunately, the pores in various layers of such composite materials cannot be distinguished using this method, or others taught by the prior art.
A new technique based on the principles of flow porometry has been developed to measure pore structure of individual layers of a composite material. The invention is described below and the analysis of results obtained with a two layered composite filtration medium is presented.
Pore structures of materials are normally determined by porosimetry or flow porometry, in which the flow occurs parallel to the thickness of the sample. Both of these techniques are incapable of determining the pore structure of individual layers of multi-layered composites. The present invention, based on flow porometry, was developed to measure the pore structure of individual layers. The present invention is described and the pore structures of two individual layers of a composite porous material, as determined by the invention, are presented herein.
Briefly stated, a method of measuring the pore structure of the individual layers in multi-layered composite porous materials includes the steps of providing a sample of a multi-layered porous material, sealing the sample in suitable test chamber, filling the pores of the sample material with a wetting liquid, such that the liquid/sample surface free energy is less than the gas/sample surface free energy, using a non-reacting gas to apply pressure to one side of the sample sealed in the test chamber, increasing the gas pressure gradually, so as to displace the liquid from the pores, and increase gas flow through the sample, measuring the pressure at which liquid flows from each successive layer of the sample material, and calculating the pore structure using an equation selected from the group consisting of p=xcex3(dS/dV), D=4 xcex3/p, and f=xe2x88x92d [100 (Fw/Fd)]d D.